Machine for processing metallic sheet and strip material



Aug. 19, 1969 J, F. WALLACE ETAL 3,461,702

MACHINE FUR PROCESSING METALLIC SHEET AND STRIP MATERIAL Filed Sept. 26, 1966 United States Patent 3,461,702 MACHINE FOR PROCESSING METALLIC SHEET AND STRIP MATERIAL John Frederick Wallace, Didcot, Roger David Butler, Kidlington, and Lancelot Alan Adkin, Didcot, England, assignors to Pressed Steel Fisher Limited, Cowley, England, a British company Filed Sept 26, 1966, Ser. No. 582,031

Int. Cl. B21b 15/00 US. Cl. 72161 1 Claim ABSTRACT OF THE DISCLOSURE A machine for suppressing the discontinuous yield point of sheet/strip metal. The metal is passed between work rolls, one covered with nylon, and plastic strain is induced.

This invention relates to a method of treating, and a machine for processing, metallic sheet and strip material, and concerns specifically a method of improving the mechanical properties of certain metallic sheet and strip material and in particular, last annealed low carbon mild steel.

It is well known that certain metallic materials, for example, last annealed low carbon mild steels, have a characteristic discontinuous yield point such that a loadextension curve for the material shows elongation occurring at a substantially constant load and this elongation is known as yield point elongation.

When such material is subjected to an operation which plastically deforms the material within its yield point elongation, deformation occurs in a non-homogeneous manner producing effects sometimes known as Liiders bends, stretcher strains, coil breaks or fluting.

These effects which occur when such metal is plastically deformed tend to destroy the smoothness of the surface of the material, such that a finished article formed from the material may be unsuitable for use when the surface appearance is important. Furthermore, a high stress is required to eifect plastic deformation of such material and this is frequently deleterious to an ensuing operation, such as a drawing or forming operation.

Hitherto, sheet or strip material having the above characteristic has been subjected to a process known as temper rolling or skin passing when the proposed use of the sheet or strip necessitates the suppression of the discontinuous yield point or the elimination of the yield point elongation. In this process a sheet or strip is passed between a pair of rolls which introduce non-homogeneous yielding at a small pitch by compression of the material in the roll gap. The machines used for this purpose have to provide a sufiicient pressure to cause a temper reduction across the width of the sheet or strip and this requires a massive structure and, of course, the rolls of the machine must be accurately profiled. Hence it has been customary for temper rolling to be effected at the steel mill producing the sheet or strip.

However, with some materials, such as rimming low carbon steel, the eifects of temper rolling are not permanent inasmuch as yield point elongation returns with time, even when the material is stored at ambient temperature, and this phenomenon is known as strain ageing. Therefore, when such sheet or strip has strain aged, subsequent to a temper rolling operation, for example when the sheet or strip has been stored for an appreciable period, it may be necessary again to suppress the discontinuous yield point by subjecting the material to a further operation known as roller levelling. During roller levelling, the material is bent over a small diameter roll known as a flex roll and/0r passed through stagger rolls. Because ice of the discontinuous yield point characteristic, as the material passes over the flex roll and/or through the stagger rolls, it kinks when suflicient bending moment has been developed by the action of the following rolls to provide a stress in the metal of sufficient value to induce yield in such a fashion as to suppress the yield point elongation which resulted from strain ageing.

It has been known, for many years, that the forming properties of aged temper rolled rimming steel sheet and coil material could be improved by passing the material through a roller leveller; however, the degree and nature of cold working provided by a roller leveller is not suflicient to produce the ductility required for deep drawing, and to suppress the yield point sufficiently to avoid the formation of stretcher strains in a formed panel in the case of materials having a pronounced yield point.

Hence, in British Patent 252,738, a machine for cold working metal sheets was proposed which included a flexing roll arrangement, adapted to impart a relatively sharp double bending to the material, in combination with a plurality of cooperating leveller rolls: however, whilst such a machine .provides a marked improvement to the cold-working properties of treated material, it has been found, in the case of last annealed rimming steels, that coil breaks occur at a pitch that is too wide for the treated material to be used for the deep drawn skin panels of vehicles. For example in the case of last annealed rimming steel sheet 0.030 inch thick it has been found impossible to induce coil breaks that are closer than 0.100 inch, and when the material is deep-drawn to form, for example, a wing or fender panel, the fluting occurring at the coil breaks is visually apparent, particularly when the panel is finished with a high gloss paint. Moreover, since such a machine must incorporate synchronised powered pinch rolls arranged to maintain the material under considerable tension as it is cold worked by the flexing rolls, the machine must necessarily be a rather costly structure.

Machines incorporating a flexing roll arrangement that comprises a roll having a resilient surface and a co-active hard roll have been known for many years; for example US. Patent 1,854,021 discloses the use of such a machine for flexing a sheet abrasive of the type having a paper or cloth backing on which is bonded abrasive particles. In US. Patent 1,930,562 there is disclosure of the use of such a machine for flexing sheet metal, and, in particular of treating a sheet metal body by progressively bending the sheet concavely and convexly beyond its elastic limit between a hard roll and a resilient roll; but the apparatus disclosed is only suitable for smoothly rounding or trueing a tubular can body by eliminating local irregularities or flats that marthe appearance of a pre-formed can. However, US. Patent 3,079,975 discloses the use of a hard roll and a resilient roll to treat metallic strip such as to induce a continuous succession of coil breaks lying close together. In the operation of the apparatus described in US. Patent 3,079,975 strip material is passed between a resilient roll and a hard roll and the pressure between the rolls is varied periodically at a frequency related to the travel of the strip such as to produce coil breaks having the required separation: but the apparatus appears to suffer from two disadvantages inasmuch as strip material treated by the machine will be curved or bowed, in the free state, by the action of the flexing rolls, and inasmuch as the apparatus is only suitable for treating strip material of a substantial length. The former disadvantage may be overcome by an apparatus disclosed in British Patent 992,527 which provides that the strip is tensioned as it passes between the hard and resilient rolls by pinch roll combinations or other pulling or retarding devices which are located ahead of and behind the flexing rolls and which pull the sheet straight. Nevertheless the use of such .pulling or retarding devices whilst overcoming the disadvantage that the treated strip is curved introduces the necessity of providing means such as pinch rolls which must firmly grip the strip between them and which must be synchronized with the flexing rolls in order to exert a sufiicient and constant tension on the strip to stress it beyond the elastic limit and thereby straighten the strip; and it will be understood that the provision of such means will add considerably to the cost and complexity of the machine.

The object of this invention is to provide a relatively simple machine for inducing closely spaced coil breaks in both strip and sheet metal.

A further object of this invention is to provide a machine for treating sheet metal which does not leave the material in curved or bowed free state.

Still another object of this invention is to provide a machine for treating strip or sheet metal which does not rely on maintaining the material under considerable tension for its effect and, therefore, does not require means for firmly gripping the material such as synchronized pinch rolls.

The invention will be further described, by way of example, wih reference to the accompanying drawing which illustrates a side elevation of a machine for carrying out the invention.

The machine includes a frame 11, on which is mounted a pair of pinch rolls 12 and 13 extending transversely across the machine; the roll 12 being carried at each end by a bearing (not shown) which has an end cap, such as 14, secured to each side of the frame 11, and the roll 13 being supported at each end by pivotable cranks each including an arm, such as 17, connected to the roll and an arm, such as 15, having one end connected to an hydraulic cylinder, such as 16, adapted to control the pressure exerted between the pair of pinch rolls 12 and 13.

Also mounted on the frame 11 is a pair of work rolls l8 and 19 extending transversely across the machine. The roll 18 is carried at each end by a bearing, such as 20, mounted within a bearing block, such as 21, and the bearing blocks are arranged to be slidable along guides, such as 22. The roll 18 is provided with two transverse backup rolls 23 each carried at each end by a self aligning roller bearing (not shown), and the bearings are mounted in plates, such as 24, one on each side of the frame 11, which are supported by a cross-beam 25 secured to the frame 11 by the plate 35 and by the nuts 26. The cross-beam 25 also supports a central bearing block 34 which is adjustable by means of set screws 27 to counteract any tendency of the back-up rolls 23 to bend. The roll 19 is carried at each end by a bearing, such as 28, within a housing, such as 29, which is secured to an arm 30; the arms 30 are pivoted at one end on trunnions, such as 31, one each side of the frame 11, and other ends of the arms 30 are each connected to an hydraulic cylinder, such as 32, adapted to apply pressure between the rolls 18 and 19.

The rolls 18 and 19 are both made of steel, the roll 18 being 3 inches in diameter and the roll 19 being 20 inches in diameter, and the roll surface of the roll 19 is covered with a /2 inch thick layer of reinforced nylon 36 having a modulus of elasticity of 1.5 p.s.i.

The frame 11 supports a stagger rolling device 33, which is known per se, and the form and operation of the device will be well known to one versed in the art and thus does not require description.

The pinch rolls 12 and 13, the Work rolls 18 and 19, and the rolls in the stagger rolling device 33 are powered by a synchronized drive means which is not illustrated but which is substantially identical to drive means currently used for driving the rollers of roller leveller machines and therefore wilt be well known to one skilled in the art, and consequently the drive means does not require to be described herein.

In operation, strip material, preferably from a decoiler, is threaded between the pinch rolls 12 and 13, work rolls 18 and 19, and the rolls of the stagger rolling device 33, the cylinders 16 and 31 are actuated to apply .pressure to the material, and the synchronized drive means operated to feed the strip between the work rolls, whereat the required plastic strain is induced, and then through the stagger rolls, where the strip is levelled or flattened.

In practice, it has been found, for example, that when a low carbon steel 20 SWG strip of deep drawing quality was processed by the machine with a pressure of 1.5 tons per inch width between the work rolls, the yield stress was reduced from 14.8 tons per square inch to 10.5 tons per square inch, whilst in the case of similar 22 SWG strip the yield stress was reduced from 15.1 tons per square inch to 10.5 tons per square inch, and in both cases the discontinuous yield point was suppressed.

What is claimed is:

1. A machine for suppressing the discontinuous yield point of sheet or strip metal including:

(a) a unitary frame,

(b) pinch roll means at one end of said frame for feeding metal of indefinite length to a flexing station,

(0) flexing station roller means comprising a hard toil and a coactive soft roll to perform the function inducing nonhomogeneous yields of small pitch in metal, said hard and soft rolls being mounted in said frame, means for applying pressure between said hard and soft rolls, back-up rolls supported by a cross-beam which is mounted on said frame, for supporting one of said hard or soft rolls.

(d) stagger roll leveler means at another end of said frame defined by a plurality of leveler rollers, a tier of leveler rollers being supported by a carrier, said carrier being adjustably mounted on said frame, another tier of leveler rollers being directly mounted on said frame,

(e) means for synchronizing the action of the pinch roll means, the flexing roll means, and the stagger roll means, whereby metal is passed through the several roller elements in the absence of considerable tension in the metal.

References Cited UNITED STATES PATENTS 2,353,375 7/1944 Todd 7216l 3,205,689 9/1965 Joseph 72146 2,742,949 4/ 1956 Nilsson 72l 61 3,079,975 3/1963 Sendzimir 72160 MILTON S. MEHR, Primary Examiner 

